1. Field of the Invention
The present invention relates to a combined sensor and bearing assembly for detecting the revolution of a rotating element used in various machines and equipments, of a type having a point-of-origin signal detecting capability that enables the detection of, for example, the rotational speed of a rotary shaft.
2. Description of the Related Art
The combined sensor and bearing assembly capable of detecting the rotational speed of one of inner and outer raceway members relative to the other thereof is currently available in various types, one of which is disclosed in, for example, the Japanese Laid-open Patent Publication No. 9-329614. However, it has been found that the rotation sensor employed in those conventional combined sensor and bearing assemblies is complicated in structure and, therefore, attempts have been suggested to provide the combined sensor and bearing assembly capable of detecting the revolution through the detection of the point of origin, which will now be discussed.
By way of example, the combined sensor and bearing assembly is suggested, in which a magnetic encoder having only a single magnetic polarity, for example, S-pole or only three magnetic polarities of N-, S- and N-poles at maximum in succession is mounted on the bearing inner race, which is a rotatable raceway member, and, on the other hand, a single magnetic sensor is mounted on the bearing outer race, which is a stationary raceway member, in face-to-face relation with the magnetic encoder. See, for example, the Japanese Patent Application No. 2003-147511. According to this suggestion, the detection of the point of origin (Z-phase) is possible and the rotational speed of the rotatable raceway member can also be detected.
The combined sensor and bearing assembly of the structure now suggested is featured in compactness, elimination of the required adjustment in assemblage and robustness and is generally used for supporting, for example, a machine drive motor.
Also, the magnetic encoder for the detection of the point of origin can be obtained by securing a magnet, which has only one magnetic polarity, to a side surface of a sealing member. In such case, this sealing member is concurrently used in the magnetic encoder and, therefore, the structure can advantageously be simplified.
However, when the combined sensor and bearing assembly having the capability of detecting the point-of-origin signal of the structure discussed above is used in the vicinity of members such as, for example, an electric drive motor and an electromagnetic clutch tending to generate a magnetic field, for detecting the rotational speed of a rotary shaft, an Hall IC element forming the magnetic sensor may be kept on under the influence of a leakage magnetic flux at all times during activation of the electromagnetic clutch, resulting in incapability of detecting the rotational.